The present invention relates to the application of thyristor chopper apparatus for determining the electric brake operation of a series propulsion motor and more particularly to control apparatus including a microprocessor that is programmed for the desired control of such thyristor chopper apparatus.
In an article entitled "Propulsion Control for Passenger Trains Provides High-Speed Service" published in the Westinghouse Engineer for September, 1970 at pages 143 to 149 and in an article entitled "Alternative Systems for Rapid Transit Propulsion and Electric Braking" published in the Westinghouse Engineer for March, 1973 at pages 34 to 41, there is described a thyristor chopper control system for propulsion and electric braking of transit vehicles. The thyristor chopper provides a propulsion system that is superior in smoothness and ease of maintaining a given speed which latter feature provides the desired automatic train control. In addition, the thyristor system makes regenerative braking practical because the response is fast enough to continuously match regenerated voltage to line voltage.
It is known in the prior art as disclosed in U.S. Pat. No. 4,095,153 of T. C. Matty et al. to use a dynamic braking control chopper apparatus for a vehicle electric motor propulsion system, with a regulator turning on the chopper when the motor current goes below a predetermined level for increasing motor current and the regulator turning off the chopper when the motor current goes above a second predetermined level for decreasing the motor current.
It is known as disclosed in U.S. Pat. No. 4,090,115 to provide a boost pulse to control the dead time around the ON control pulse in relation to the OFF control pulse of the main chopper for controlling the commutation circuit of the main thyristor. This commutation circuit requires a predetermined time interval to be established to prevent the firing ON of the main thyristor while the commutation circuit is operative relative to the commutation thyristor. The actual time length of the provided control boost pulse is determined by the required length of time for the associated program software to be executed for providing this boost pulse function. A microprocessor permits changing the execution path in the program to control the start time of the boost pulse, which is the last time an OFF pulse can be fired, and to control the start time of the ON pulse positioned in relation to the middle of the boost pulse. The trailing edge of each boost pulse is the first place the next OFF pulse can be fired to protect against running the OFF pulse into the next ON pulse and to protect against running the last ON pulse into the next OFF pulse. This avoids any problem with the thyristor memory to assure that the proper thyristor goes ON when desired. If the desired thyristor were not fired ON at the proper time, this could result in an undesired positive feedback operation to lock up the chopper system with the main chopper not functioning as desired.